Forest Health Hot Topics

Spruce beetle
Actual size: ~1/4 inch
S. Valley, OR Dept of Ag
Bugwood.org

Spruce beetle is always present in our spruce forests and has a notorious history in Alaska. In times of low populations, spruce beetle favors large diameter, wind-thrown or otherwise damaged spruce trees. Spruce beetle is capable of killing otherwise healthy spruce, though, when populations are high. Long-time residents may remember the spruce beetle outbreak in the 1990s. At the peak of the outbreak, in 1996, spruce beetle-caused tree mortality was observed on more than one million acres.

Since 2011, observed spruce beetle mortality statewide had been relatively low. Recent surveys, however, detected a dramatic increase in spruce beetle activity in several areas of Southcentral Alaska.

Northern spruce engraver
Actual size: ~3/16 inch
Pest and Disease Image Library
Bugwood.org

Spruce beetle damage is typically less extensive in Interior Alaska. There, the northern spruce engraver is commonly observed causing damage to spruce. From May through July, northern spruce engravers actively attack white spruce weakened by wind, fire, flooding, or other stressors. Fresh cut spruce and spruce slash from land clearing or forest management activities may also be susceptible. 

Northern spruce engraver populations are being closely monitored in the Tanana River valley. A 2012 windstorm in that area left large areas of spruce blown down, broken, or leaning. Increased amounts of northern spruce engraver-caused white spruce mortality have been observed in these wind-impacted forests recently. 

Northern spruce engraver Forest Insect and Disease Leaflet

Spruce Aphid - The non-native spruce aphid primarily infests Sitka spruce as well as ornamental spruce in coastal areas. While some trees may be killed in severe infestations, most affected trees survive. Aphid-caused defoliation can weaken trees, potentially making them more susceptible to other forest health threats.

The current known range of spruce aphid in Alaska includes Southeast Alaska, Prince William Sound, the Kodiak Archipelago, and the Kenai Peninsula. 

Integrated Pest Management Issues - Spruce aphid
(University of Alaska Fairbanks – Cooperative Extension Service)

Spruce aphids
Alaska Division of Forestry

Defoliated willow, alder, and birch
Upper Yentna River valley
Alaska Division of Forestry

Recent aerial surveys noted ongoing generalist defoliation in several areas. This defoliation is occurring in parts of the Alaska Range, Aleutian Range, and multiple locations in Southwestern Alaska. Recent evidence suggests that the native moth, Orthosia hibisci,is responsible for the defoliation in at least some of the impacted areas. DNA-based investigations into the insect or insects responsible will continue.